In the construction of machine tools it is common practice to mount the cutting tool on the free end of a ram which is slidable in a bearing member during the machining operation. An example of such construction is found in vertical boring mills in which the workpiece is clamped on a rotating table and in which the ram advances vertically toward the workpiece to generate a surface of revolution. Since the supporting bearing for the beam remains relatively fixed during the advance of the ram, the unsupported portion of the ram changes in length during machining. This means that, even though the cutting force remains the same as the tool advances axially along the workpiece, the length of the cantilever represented by the unsupported length of the ram changes. For instance, if the surface of revolution is a bore, the ram advances vertically through the bore in an axial direction with the tool directed outwardly to generate the desired surface. If the amount of metal being removed from the surface of the bore is the same from top to bottom, the force on the tool will remain the same, but the length of the cantilever represented by the unsupported portion of the ram becomes longer and longer as the ram advances downwardly. This means that the amount of deflection of the ram will increase as it advances downwardly. This also means that the surface generated by the tool will be tapered in an undesirable manner. Complex control mechanisms can be used to move the ram and its tool laterally to compensate for such taper, but they are both expensive and delicate and do not entirely overcome the problem. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a machine tool in which the ram which carries the cutting tool is stiffened without substantially increasing its weight in an amount commensurate with the stiffness added and in which the amount of stiffness added can be adjusted to suit the circumstances with which it is to be used.
Another object of this invention is the provision of a machine tool in which means is provided to compensate for any variation in the amount of deflection of a ram due to change in its unsupported length.
A further object of the present invention is the provision of a machine tool having stiffening means for the ram, which means is simple and inexpensive and which is capable of a long life of useful service with a minimum of attention.
It is another object of the instant invention to provide a machine tool for generating a surface of revolution which surface is free of undesirable taper.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.